Methods of surface-treating hook members of metal slide fasteners and slide fasteners thus obtained



Feb. 17, 1970 o1 N 3,496,004

METHODS OF SURFACE-TREATING HOOK MEMBERS OF METAL SLIDE FASTENERSAND'SLIDE FASTENERS THUS OBTAINED I Filed June. 24. 1966 United StatesPatent Int. Cl. B32b 15/02 U.S. Cl. 117-130 3 Claims ABSTRACT OF THEDISCLOSURE A method of coating slide fasteners having hooking elementsof copper or alloys of copper, zinc or alloys of zinc, iron or alloys ofiron, after mounting upon the textile support and without havingrecourse to an electric current or to an exterior source of electricitywith a coating of tin, cadmium or antimony. The fasteners are immersedwith their textile support in a complex solution possessing a highelectrical potential of tin, cadmium or antimony. The solution has a pHlower than 12 and the temperature is lower than 60 C. and preferablybetween 30 and 60 C. t

This invention is concerned with improvements in the surface treatmentof interlocking or hook members of metal slide fasteners.

It is known that most slide fasteners or zippers consist of interlockingmembers obtained by cutting, stamping or injection from wires, flatsections or like stock of copper alloys (such as tombacs and brasses),aluminum alloys such as scleral or duralinox, or zinc alloys.

According to conventional and old manufacturing methods, these membersare barrel-polished and possibly nickel-plated, if stainless slidefasteners are desired, and subsequently get along the edges of textiletapes or ribbons by using so-called sorting machines.

It may be noted that nickel-plating (by reduction of nickel ions) andbronzing (by surface oxidation) according to conventional method, asapplied to the abovementioned interlocking members, are still the onlysurface treatments utilized for copper-alloy or zinc-alloy slidefasteners. More particularly, cadmium plating was never applied owingmost probably to its high cost and to the special cares requiredtherefor, and on the other hand the direct chromium plating of thesehook members is impracticable in the case of loose small parts.Regarding tinning, this technique was also disregarded due to thereadily available advantages and great simplicity characterising thegalvanic nickel plating treatment.

At present automatic, high-efficiency machines are increasingly used forsimultaneously stamping, cutting and setting the hook members of slidefasteners. Of course, it is no more possible, as contrasted with thehitherto conventional practice, to nickel plate the metal elements ofslide fasteners made of copper alloys. Neither could these elements becoated with any protective metallic layer.

Actually, methods of making electrically conducting separate orassembled strips constituting a slide fastener have been developed andcarried out in practice, with a view to permit the surface treatment oftheir component elements by galvanizing, but, save for one exception, ithas not been possible to prepare electrolytic solutions preserving theintegrity of the dyes and/or fibres of the textile support. The onlyresult thus achieved, under certain specific conditions, was a combinedcopper and tin coating of copper-alloy slide fastener elements, thecombination of these two metals proving to be necessary 3,496,004Patented Feb. 17, 1970 for conductivity reasons. Furthermore in thisrespect, it should be noted that the desired coating does not catch onthe inner side of the hook portions of the interlocking elements set onthe textile ribbons, for galvanic treatments become ineffective orscarcely effective when it is desired to form metal coatings incavities.

However, slide fasteners, whether they are obtained according to the oldmethod or by applying the new method, consist of hook or interlockingmembers having a high coefficient of friction, in spite of the polishingoperations to which they may be subjected, this coeflicient of frictionbeing detrimental to the movements of the sliding element andaccelerating the wear thereof, and, therefore, the useful life of theslide fastener. Although nickel plating as applied by the conventionalmethods of galvanizing to the interlocking members obtained according tothe old manufacturing methods will properly protect slide fasteners fromoxidation, it cannot overcome the inconvenience set forth hereinabove.The same applies to the above-mentioned combined copper-tin coatingmethod.

Now it was found in the course of many tests having led to the presentinvention, that a very satisfactory sliding movement of the slidingmember could be obtained, even without preliminary polishing the hookmembers, by coating these members with tin or antimony, or cadmium, orcadmium and tin, or antimony and tin, or vice versa, these three metalsactually combining a high resistance to corrosive and oxidizing agentswith selflubricating properties which up to now have neither beenevidenced nor utilized.

Under these conditions it is one object of this invention to provide, byway of novel industrial products, slide fasteners wherein theinterlocking metal members are tinned, that is, coated with a more orless thick layer of tin. The term tinned as used herein designatescoatings of metals namely tin coatings of antimony, cadmium, as well asantimony and tin coatings, cadmium and tin coatings, and vice-versa,these last named coatings being applied in the form of successivelayers.

According to this invention, sliding fasteners can be tinned at anydesired stage of their manufacture, notably when the interlockingmembers are completely finished, even when the left-hand and right-handmembers of the slide fastener are in their interlocked position. Theconditions in which the surface treatment can be applied will bedescribed hereinafter.

This invention, as far as the aforesaid three metals: tin, cadmium andantimony, is concerned, is applicable to all types of sliding fastenerscomprising copper or copper-alloy interlocking members, and in thespecific case of tin and cadmium, to all types of sliding fastenershaving zinc and zinc-alloy interlocking members.

.On the other hand it is known that the metals utilized in themanufacture of sliding fasteners are copper alloys, aluminium alloys,zinc alloys, or in the case of spira fasteners, brass wires orstainless-steel wires. It is not ap parent, so far, that it has beenpossible to manufacture commercial-quality sliding fasteners from ironor mild steel stock, in spite of the considerable advantages likely tobe derived from the use of these materials, due to the lower cost offerrous metals in comparison with that of non-ferrous metals.

The present invention, as will be explained presently (and this alsoconstitutes one of its objects), permits of utilizing iron and iron orferrous alloys in the industry of sliding fasteners by resorting to asuitable coating of tin and/ or cadmium and/or antimony, the iron oriron-alloy inter-locking members of the sliding fastener which are thuscoated and protected having a remarkable resistance to corrosion andoxidation. 4

, The present invention therefore includes the timing.

(taken in the meaning given hereinabove) of sliding fasteners made ofwhich the metallic elements consist of met- 11s, namely: copper andcopper alloys, zinc and zinc alloys,

iron and ferrous alloys,'by using coatings of antimony, b

:admium and/ or tin in single or multiple layers of one 9f these metals,or successive and/ or alternating layers of two or three of said metals.

In this respect it will be noted that the use of suitable metal ionsolutions acting without the intervention of elec-;

tric current, as will be described presently, will coat all the parts ofthe, interlocking members, including the inner faces of the lugs set onthe tapes or ribbons, the liquid impregnating these faces bycapillarity,the metal ions being deposited without difficulty.

Finally, it will be noted that if antimony is used alone or in admixturewith metal salt dyestuffs it permits of 0btaining not by surfaceoxidation but by metal coating the bronzing of slide fasteners, notablythose intended for military use. Depositing a layer of antimony ontombac 5 interlocking members for bronzing or browning same as requiredfor military use increases in very considerable proportions the numberof to-and-fro movements of the brass sliding member, also req iiredfor'the same use,

which the sliding fastener may Withstand before displaying any'appreciable wear.

Regarding the practical embodiment ofthis invention,

a distinction should be made between on the one hand the various methodsof manufacturing metal sliding fasteners and ontthe other: hand thevarious solutions likely to be used--whether electrolytic or withoutusingelectric current for producing'the desired coatings of tin and/0rcadmium and/ or antimony.

(A) ELECTROLYTIC PRo'cEssEs them, the tinning, cadmium-plating ofordinary metals, as

well as antimony coating, being well known in the art of galvanizing.

Tin, by combining its Well known corrosion resistance with aself-lubricating property particularly advantageous as far as theoperation of the sliding member along the interlocking members isconcerned, will thus constitute an ideal substitute for nickel; ifdesired, it may be either superposed to the nickel or, finally, combinedtherewith according to known processes for simultaneously depositing tinand nickel.

However, it should be emphasized that the subsequent steps of settingthe interlocking members on the ribbons are likely to develop cracks inthe protective coating and therefore lead to small patches, points orincipient rupture lines open to corrosion. Under these conditions itwill be specially recommended, according to this invention and in thecase of iron or iron-alloy sliding fasteners, to coat the interlockingmembers with an extremely or relatively thick protective layer so thatthe latter cannot be deeply It will be noted that a fine crystallizationof the deposits wiil reduce the risks of cracking the .coating whensetting the interlocking members on the textile supports.

(2) In the case of manufacturing methods wherein the interlockingmembers are simultaneously out and set on the textile supports, theseparate or assembled strips constituting the sliding fastener beingunsuitable for conducting current, some means must be provided forensuring the continuityriof the contact between the interlockingmembers. This feature may be obtained by introducing a conducting wire,for example of aluminium or copper, or a cord or braid surrounded by acoiled aluminium sheath of film, either into the marginaLbead of thetextile support in which the interlocking members are set, or betweenthe ribbon and the interlocking members when manufacturing theslidingfastener; as practised in the anode oxidation of aluminium orlight-alloy sliding fasteners. The continuity of the electric contact:between the interlocking members may also be obtained by frictional orsliding contact with a metal conducting wire gauze or with conductingmetal rolls or in any other suitable manner. a

The electrolytic baths utilized may be those well known in galvanizingfor depositing the metals contemplated in the present invention, butthese baths having high concentration of metal salts and being extremelyalkaline (tin-cadmium) or very acid (antimony) are obviously noxious tothe dyes applied to the textile support and also the strength of thetextile fibres incorporated therein, which may even preclude the use ofraw or unbleached ribbons. Moreover, the poatings will be deposited.with a certain slowness and the elimination of bases and cyanides willrequire particular care. 7 i 7,

Under these conditions, it will be preferable to treat sliding fastenersin the form of separate or assembled strips, especially iron andferrous-alloy sliding fastenings, according toihe non-electrolyticmethods to be disclosed presently. 1

However, in the specific case of tin, a diluted bath that will not bedetrimental to the ribbon dye may be used without inconvenience. Atypical bath of this character may have the following composition:

Water liter 1 Tinchloride gr./liter 10 Trisodic phosphate do 45 Sodiumcyanide do 10 Temperature C 30 to 35 pH 10 to 12 Of course, this is butan example and the proportion of the ingredients as well as theoperating temperatures may vary within very wide limits. The trisodicphosphate may be replaced wholly or partly by'another alkaline affectedby the setting operation. An advantageous method of combining thisrequirement with a bright appearance and a low cost of the slidingfastener, will consist in coating the interlocking members with asuitable layer of zinc or cadmium and to coat this layer in turn with afinishing tin layer to impart a bright appearance to the article.

, two microns.

(B) NON-ELECTRGLYTIC, SO-CALLED IMMER- SION PROCESSES (1) Chemicaldispiacement, process It is known that if a metal is immersed into asolution of a salt of another metal having a higher rank in the scale ofelectrolytic values, the surface of the first metal will become undercertain conditions coated with a more orless thin layer of the secondmetal.

However, these solutions operate at relatively high temperatures rangingfrom to C., and therefore they detrimentally affect the dyes of ribbonsor other textile supports. Under these conditions it will be necessaryto either operate on raw or unbleached ribbons, or brightening up thedyes after the treatment.

Moreover, although the metal deposits vary rapidly, its

thickness seldom exceeds one-tenth of a micron, since an electrolyticequilibrium develops between the solution and the immersed metal as soonas the latter becomes coated with a metal film containing said solution.

In the case of zinc and zinc alloys, their behaviour is the same as thatof copper and its alloys.

Regarding iron and ferrous alloys, these may cause the displacement ofantimony ions in very acid solution.

In the present state of our knowledges, and save for the aforementionedexception, depositing cadmium or antimony by chemical displacement isstill unknown.

It will therefore be preferable, in most cases, to resort to improvedprocesses of the so-called simple immersion type by using solutions ofmetallic complexes for depositing antimony and tin, and to improvedprocesses also of the so-called immersion type by using a contact metalfor depositing cadmium and possibly tin.

(2) Simple immersion process It is known that complexes consist eitherof the coordination of several radical atoms or molecules about acentral metal atom (perfect complex), or of molecular combinations(imperfect complex), which coordination or combination involves anincrement in the electric charges of the metal ions and therefore amodification in the electrolytic potential of the complexed solution. Atypical complex may be for instance the combination of metal saltseither with other metal salts or 'with neutral molecules (hydratesammonia, sodium or potassium chloride, organic amines, cyanides,tartrates, citratcs, thiourea, glycocoll, etc.).

According to the present invention complexes having the highest possibleelectrolytic potential will be used,

By way of example, the following complexed solution may be used fordepositing pure tin on brass and tombac sliding fasteners:

Sodium tartrate and potassium tartrate develop with stannous chloride acomplex sodium cyanide salt and leads to a solution. By operating atabout 35 C., 1 to 2 microns of tins will be deposited within 20 minutes.

This is a complex in a state of unstable equilibrium; in other words,the relationship of its component elements does not adhere to the normalstructural equation. These compounds are particularly active andreactive for being in a state of unstable equilibrium they can easilyabsorb or lose electrons, thus modifying their oxidation degree or thatof the products with which they are put into contact.

The abovespecified bath (in a state of unstable equilibrium), even inthe advocated diluted form according to this invention, will prove moreactive for the purpose contemplated than more concentrated solutions butin a state of stable equilibrium. v

The following formula exemplifies a typical complex in a. state ofrelatively stable equilibrium:

Gr./liter Stannous chloride 2.5 Tartric acid 0.5 Sodium pyrophosphate 15Sodium cyanide 6 H O to make one liter.

for example a few grammes per liter, will accelerate the tin depositwhile affording somewhat thicker coatings.

It is also possible to use cyanide-free solutions which are particularlyadvantageous considering the danger constituted by the handling of thissubstance and the difficulty of completely eliminating it from thetextile supports of the sliding fasteners.

In this case, it is only necessary to complex for' example tin chlorideeither with double sodium tartrate and potassium tartrate and thiourea,or with tartric acid and thiourea.

The best conditions of use of these complex tin solutions are a pH valueranging from 8 to 9 and a temperature ranging from 30 to 40 C.

In the case of antimony, various salts of this metal, such as antimonytrichloride, antimony trioxide, metaantimonious acid, etc. will be usedby complexing them with citric acid, potassium citrate, thiourea, etc.

By way of example, the following formula may be used:

H 0 to make one liter.

The optimum conditions of use of complex antimony solutions are a pHvalue ranging from 1 to 3 and a temperature ranging from 50 to C.

(3) Immersion process with a contact metal It is known that if a metalto be metallized by immersion is caused to contact another,electronegative metal, mostly zinc or aluminium and their alloys in anaqueous solution of metallic ions expected to provide the desiredcoating, the metallic ions will form on the metal to be coated a layerthicker than those obtained by simple immersion, but these ions are thusalso deposited on the contact metal which becomes very rapidly passiveand loses is efficiency immediately as a thin metal film builds upthereon.

The thickness of the coatings likely to be thus obtained althoughgreater than that of the coatings obtained by simple immersion, is nonethe less limited and under the best conditions it cannot exceed a fewmicrons.

According to this invention aluminium and its alloys are used preferablyas contact metals and the passivation of the contact metal is avoided byattacking the aluminium or alloyutilized in the process by incorporatingsoda or potash into the complexed solution, either directly orindirectly by hydrolysis of a suitable alkaline salt.

Under the influence of the base, the aluminium will form an aluminatesolution with consequent release of hydrogen in the nascent state whichactivates the reduction of the metal complexes thus dissolved. Moreover,an essential fact to be noted is that the release of hydrogen, through asomewhat mechanical or physical action, prevents the dissolved metallicions from depositing on the contact surface which thus remains active.Finally, if aluminate ions are released, they will not adhere to thesurface to be treated and therefore they will not interfere with thedesired deposit or coating.

In practice, the necessary contact may be ensured by one of theprocesses described hereinabove in Section 1, but it will beadvantageous, due to the simplicity of the operation, during themanufacture of the sliding fastener to insert a contact wire between theinterlocking members of the sliding fasteners. This wire may consist ofa single aluminium or aluminium-alloy filament, or a textile cord ofcotton or like material, coated with a thin film of aluminium oraluminium-alloy.

It is worth pointing out that according to this invention and ascontrasted with current requirements in the matter of anode oxidation,the contact wire can be broken very frequently, provided that onefragment of the contact wire contacts each member of the slidingfastener, and

the desired effect will be obtained nevertheless. It is even onlynecessary, when treating the two assembled strips constituting thesliding fastener, that one fragment of the contact wire contacts one ofthe interlocking members The minimum amount of soda should be added inorder to attack the contact wire without inasmuch damaging the ribbondye, this amount being of the order of 1 to 2%.

Solutions without cyanide of the type set forth hereinabove may also beused by adding a base thereto It is only necessary to complex, say, tinchloride, with Rochelle salt and/or thiorea, and to add a base as setforth hereinabove.

In the case of cadmium, salts such as cadmium oxide or cadmium sulfatemay be used, which will be complexed according to the conventionalmethods of making complexes, as exemplified hereinabove.

The following formula may be used:

Gr./ Liter Cadmium sulfate CdSO 8/3H O 7.5 Double sodium and potassiumtartrate 40 20 Caustic soda Water to make one liter.

(C) FEATURES CHARACTERISING THE IMMER- SION PROCESSES, OF THISINVENTION, WITH OR WI I HOUT CONTACT (1) Of course, the above-describedcomplexes correspond to well-defined formulae. However, the proportionsof the component elements may be modified without major inconveniences.The component elements in excess will not complex but will not inasmuchcompromise the action exerted by the solution, provided that they do notprecipitate on the contact metal or the surfaces to be treated.

(2) The complexes operate under very variable tem-.

perature conditions, ranging from room temperature to the boiling pointor a temperature approximating this point.

(3) The "complexes operate under very variable concentration conditions,their dilution attaining up. to a few grams per liter of chemicals.

(4) Under the optimum conditions, the complexes advocated herein areclear or slightly cloudy, and will not or little affect the dyes or thetextile fibres.

(5) The rate of concentration of the baseused in the composition of thesolutions implemented in the contact processes is quite variable, thelower limit being the attack of the contact metal and the release ofhydrogen, the upper limit being the instability of the solution and theturning of the dyes.

It is therefore possible to combine the solution with the temperatureand other conditions as a function of the specific conditions ofmanufacture of the sliding fasteners (i.e. thickness of the desiredcoating films, rate of 8. deposit, dye quality, etc.) without departingfrom the spirit and scope of the invention as set forth in the appendedclaims.

In the attached drawings, FIGURE 1 illustrates diagrammatically by wayof example a sliding fastener of a well-known type comprising metalinterlocking members 10 and 11 set on supporting ribbons or tapes 12 and13, and a sliding member 14. The contact metal consists of aluminiumwires 16 and 17 threaded between the interlocking members and theribbons or tapes.

FIGURE 2 illustrates on a larger scale and in crosssectional view asingle hook member 10 coated with a tin layer 18according to the methodof the present invention.

FIGURE 3 illustrates similarly on a larger scale that the contact metalconsists of a thin aluminium film 19 coiled around a cotton wick or likecord 20.

What I claim is:

1. A method of coating slide fasteners having hooking elements ofcopper, zinc, iron or the alloys thereof, mounted upon a textile supportwithout recourse to an electric current or to an exterior source ofelectricity with a coating of tin, cadmium or antimony comprisingimmersing said fasteners with their textile support in a complexsolution having a high electrical potential containing a. metal selectedfrom the group consisting of tin, cadmium and antimony, said solutionhaving a pH lower than 12 and the temperature being between 30 and 60 C.and comprising a strong base in a quantity between 1 to 2% of the totalvolume of said solution, the elements of said slide fasteners beingplaced in contact with an electronegative metal taken from a groupconsisting of aluminum, magnesium or their alloys.

2. A method according to claim 1 in which said electronegative metalisaluminum in the form of an aluminum or aluminum alloy wire, wound abouta textile wick, said wire being inserted between said hooking elementsand said textile support during the fastening thereof.

3. A method of coating slide fasteners having hooking elements ofcopper, zinc, iron or the alloys thereof, mounted upon a textile supportwithout recourse to an electric current or to an exterior source ofelectricity with a coating of tin, cadmium 0r antimony comprisingimmersing said fasteners with their textile support in a complexsolution having a high electrical potential con- 4 .1 taining a metalselected from the group conisting of tin,

cadmium and antimony, said solution having a pH lower than 12 and thetemperature being between 30 and 60" C., said complex solution beingcarried out in the presence of an electronegative contact metal in asolution such as aluminum, magnesium or their alloys to increase thenecessary electric potential by displacing the coating metal, and saidcontact metal being aluminum in the form of an aluminum or aluminumalloy wire wound about a textile wick inserted betwen the hookingelements and the textile Supportduring the fastening thereof.

- References Cited .UNITED STATES PATENTS 2,264,324 12/1941 Morin24-205.16 2,264,580 12/1941 M orin 24205.l6 2,326,707 8/1943 Thomas2041l9 3,072,498 1/1963 Knowles et a1. 117-430 X 2,159,510 5/1939Pavlish et a1 1l7l30 2,282,511 5/1942 Bradley 1l7130 2,369,620 2/1945Sullivan et al. ll7-130 2,735,788 2/1956 Lowenheim et al. 117130 FOREIGNPATENTS 955,775 4/1964 Great Britain.

RALPH s. KENDALL, Primary Examiner U.S. ci. X.R.

